The present invention relates to a noncontacting face seal, and more particularly to a noncontacting face seal in which an end face of a rotating sealing ring rotatable with a rotating shaft and an end face of a stationary sealing ring facing the rotating sealing ring form sealing surfaces for restricting a fluid flow from a high pressure side to a low pressure side.
A noncontacting end face seal (hereinafter referred to as end face seal) is used for sealing the space between a rotating shaft and a housing thereof. The end face seal is incorporated in, for example, gas turbines or compressors which handle high pressure. In general, there are two types of noncontacting end face seals, one of which is a hydrostatic end face seal using the pressure of sealing fluid, the other of which is a hydrodynamic end face seal having a shape causing hydrodynamic action such as spiral grooves.
Next, the conventional hydrostatic end face seal will be described below with reference to FIGS. 12 and 13.
The end face seal comprises two annular sealing rings facing one another, one of which is a rotating sealing ring 3, the other of which is a stationary sealing ring 4. A rotating shaft 1 accommodated in a housing 9 is provided with a sleeve 2. The sleeve 2 is connected to the rotating sealing ring 3 through a pin. The stationary sealing ring 4 is pressed against the rotating sealing ring 3 by an urging force of springs 10 interposed between a sealing ring retainer 5 and a spring retainer 6. In the end face seal, the radially outer region of the rotating sealing ring 3 is located at a high pressure fluid side H and the radially inner region thereof is located at a low pressure fluid side L. The rotating sealing ring 3 is provided with an outwardly tapered surface 31 which makes the gap between the rotating sealing ring 3 and the stationary sealing ring 4 wider gradually. That is, the tapered surface 31 provides the necessary wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4 at the radially outer regions thereof for introducing fluid between two sealing rings. The rotating sealing ring 3 is further provided with a flat surface 32 inside the tapered surface 31.
In the end face seal of this type, when fluid enters into the wedge-shaped space between the rotating sealing ring 3 and the stationary sealing ring 4, the sealing surfaces are moved out of contact by hydrostatic forces from fluid pressure. The distance e between the outer edge of the tapered surface 31 of the rotating sealing ring 3 and the sealing surface of the stationary sealing ring 4, the inner diameter 2r.sub.t of the tapered surface 31, the inside diameter 2r.sub.1 of the sealing surface and the outside diameter 2r.sub.2 of the sealing surface are properly arranged so that the gap between the sealing surfaces becomes as small as possible and the stiffness of the fluid film formed between the sealing surfaces is enhanced.
In the conventional end face seal as shown in FIGS. 12 and 13, in order to reduce leakage of fluid between the sealing surfaces, it is necessary to make the gap of the sealing surfaces small. However, there is a limit to how much the gap can be reduced. Therefore, in the end face seal of this type, it is difficult to reduce the leakage of fluid beyond a certain amount.
On the other hand, another type of end face seal with spiral grooves is disclosed in U.S. Pat. No. 3,499,653. In U.S. Pat. No. 3,499,653 the end face seal comprises a rotating sealing ring and a stationary sealing ring as with the end face seal in FIGS. 11 and 12. One of the sealing rings has spiral grooves and a tapered surface to provide the necessary wedge-shaped space at the radially outer regions thereof. The spiral grooves extend from a high pressure fluid side to a low pressure fluid side so as to pump fluid from the high pressure side to the low pressure side. Under normal operation, the fluid film is formed between the sealing surfaces by hydrostatic action and hydrodynamic action, thereby restricting fluid flow from the high pressure side to the low pressure side.
However, in the above end face seal, the spiral grooves extend from the high pressure side to the low pressure side so as to pump fluid from the high pressure side towards the low pressure side. Therefore, under dynamic conditions, the spiral grooves serve to leak fluid from the high pressure side to the low pressure side. That is, the total leakage rate of fluid from the sealing surfaces is equal to the leakage rate caused by the pressure difference between the high pressure and the low pressure plus the leakage rate caused by the pumping action of the spiral grooves. Consequently, in the end face seal of this type, it is difficult to reduce leakage of fluid beyond a certain amount less as with the end face seal in FIGS. 12 and 13.